The MS community — researchers, physicians, and patients alike — has been interested in vitamin D for some time, and recent studies suggest that low vitamin D levels might increase a person’s risk for developing MS.

But if you’ve already been diagnosed with the disease, should you worry about your vitamin D levels, and should you be taking a supplement? Research on these questions is still ongoing, but here’s what we know so far:

Vitamin D Deficiency Is Common in People With MS

Studies show that people with newly diagnosed multiple sclerosis tend to have low vitamin D levels. The same is true for people with clinically isolated syndrome (CIS), a first episode of neurological symptoms associated with demyelination, which can progress to MS.

“It is rare that I find a patient that has a normal level without supplementation,” says Claire Riley, MD, a neurologist and medical director of the Multiple Sclerosis Clinical Care and Research Center at Columbia University in New York City.

There are several possible explanations for low vitamin D in people with MS. Genetic studies show that genes linked to low vitamin D are more common in people with MS, and they may also have differences in intestinal absorption of the vitamin. A study published in May 2016 in the journal Multiple Sclerosis found that when people with MS took a vitamin D supplement for three months, their blood levels didn’t rise as much as those of people without MS.

As the disease progresses, people with MS may also spend less time outside if heat aggravates their symptoms or disability interferes with physical activity, and lack of sun exposure could put them at further risk for vitamin D deficiency.

Higher Vitamin D Levels Linked to Better Outcomes

A study published in March 2014 in the journal JAMA Neurology found that in people diagnosed with CIS, having higher vitamin D levels was associated with a lower chance of developing MS. And in people who did develop MS, higher vitamin D was correlated with fewer relapses and a slower progression of disability, an observation that had been made in previous studies. Together, those studies suggest that when people with MS have vitamin D levels of 40 to 60 nanograms per milliliter (ng/mL), they tend to have better outcomes.

But a more recent study, published in June 2016 in the journal PLOS One, suggested that this protective effect of vitamin D may be limited to younger people in earlier stages of MS. Over three years of the study, there was no effect of vitamin D levels on disability progression. Higher vitamin D levels were associated with fewer relapses, but only in people younger than 38.

Will Taking a Vitamin D Supplement Help People With MS?

This question doesn’t yet have a clear answer.

So far, most of the evidence on vitamin D and MS has come from observational studies, which look at correlations between existing blood vitamin D levels and the disease. Randomized controlled trials, in which participants are randomly assigned to receive a potential treatment or a placebo, are considered a more rigorous way to prove efficacy of a potential treatment, but unfortunately, only a few randomized trials have tried to answer the question of whether vitamin D supplementation is truly beneficial in people with MS. The results were mixed, with some finding small benefits and others not. Still, many doctors are already recommending supplements to their patients.

“Those studies are sort of collectively suggesting that there does appear to be some benefit for people with MS who use vitamin D supplements,” says Kassandra Munger, doctor of science in nutritional epidemiology and a research scientist at Harvard T.H. Chan School of Public Health in Boston. “There are some clinical trials under way right now to look more in depth at these questions,” she adds.

Ongoing trials include the VIDAMS study, led by researchers at Johns Hopkins University in Baltimore. The study is still recruiting participants at centers around the country, including Columbia University, where Dr. Riley heads up involvement in the study.

Doses Vary as Practitioners Recommend Vitamin D

Riley says that she is waiting on the results of this trial so that she can advise patients with more certainty. But until then, “I think the informal consensus is to supplement patients so that they are in the high end of normal range,” says Riley. If patients are deficient in vitamin D, she often starts with a high dose to correct the deficiency and then recommends 2,000 IU (international units) of vitamin D per day, adjusting as needed with a goal of maintaining blood levels around 50 ng/mL.

In a review published in May of 2017 in the journal Multiple Sclerosis and Related Disorders, French researchers Charles Pierrot-Deseilligny and Jean-Claude Souberbielle wrote, “From a pragmatic and practical point of view, while waiting for new scientific information, a vitamin D3 supplementation using moderate oral doses (between 2,000 and 4,000 IU per day) can already be undertaken in all types of MS patients, including pregnant women.”

Sharon Stoll, DO, an assistant professor of neurology at Yale School of Medicine in New Haven, Connecticut, takes a slightly more aggressive approach, recommending 5,000 IU per day to maintain high blood levels. “I make sure all of my patients are on supplements,” she says. “We have no cure for MS, so any additional treatment I think is worth trying.”

The VIDAMS trial is also using a dose of 5,000 IU per day, while two European trials are using doses of 10,200 IU and 14,000 IU per day.

Kidney Stones Potential Consequence of Too Much Vitamin D

These supplementation levels are higher than those recommended for healthy people by the Institute of Medicine, which estimates that most people need about 600 IU of vitamin D per day and says anything more than 4,000 IU per day is too much. One concern is that high doses of vitamin D could cause kidney stones, “but my experience is that these are quite rare,” says Riley.

Several small studies have looked at the safety of high-dose vitamin D supplements in MS patients with reassuring results, but the results of VIDAMS and other clinical trials will provide more information about the risks and benefits of taking vitamin D.

For patients and their doctors making health decisions with incomplete information, those study results can’t come soon enough.